Protective relay circuitry for hoist motor controls



June 1, 1965 H. G. GARTEN 3,187,246

Original Filed Nov. 8, 1957 2 Sheets-Sheet l L| L2 +||ov. Z2 20 .5SERIES FIELD OVERLOAD RELAY VE IQQmJ RELAY 0 HOIST orr LOWER 577; 12 4514 I i ,2" I E w 5 l l' i T T Mira iH! w m H i i H'T I n 7 1 l l 2% IIl'5Il;:T m l "mm-WT w i wil m: i Hui-g wn 1 I g s I i I ++1+ +43% 'I'I-IP' HT C/ I II I I O M. --II CONTACT "0mm OPEN umav'w ifi tin )F-CONTACT NORMALLY CLOSED O- RELAY COIL A TTORNE Y D RESISTOR June 1, 1965TE 3,187,246

PROTECTIVE RELAY CIRCUITRY FOR HOIST MOTOR CONTROLS Original Filed Nov.8, 1957 OFF POSITION INVENTOR. HARRY G. GARTEN ATTOQAG'Y 2 Sheets-Sheet2 United States Patent PROTECTIVE RELAY CIRCUITRY FOR HOIST MOTORCONTROLS Harry G. Garten, Alloy, W. Va., assignor to Union CarbideCorporation, a corporation of New York Original application Nov. 8,1957, Ser. No. 695,282 new Patent No. 3,021,465, dated Feb. 13, 1962.Divided and this application Apr. 19, 1961, Ser. No. 104,101

1 Claim. (Cl. 318247) This is a division of application Serial No.695,282, filed November 8, 1957; now Patent No. 3,021,465 dated February13, 1962.

This invention relates to a protective circuitry for use with directcurrent hoist motors and controllers therefor on overhead cranes and thelike. More particularly, it relates to a relay circuit which preventsloss of control of the motor during lowering due to a failure in thatportion of the armature circuit which is common to the field circuit.

Industrial power applications require crane hoisting motors which mustbe able to withstand rigorous extremes of operating conditions. Themotors and their associated control circuits must be capable of handlingheavy loads while maintaining a high degree of control at all times. Inaddition, the motors and control circuits are subjected to extremelyhigh currents and often operate in highly corrosive atmospheres both ofwhich adversely affect conductive contacts and the control elementsthemselves and can result in periodic circuit failures.

The type of motor most often employed for operation of the hoistingmechanism of various cranes is the series wound DC. motor. The seriesmotor is admirably adapted to the purpose because of its inherentcharacteristic of adjusting its speed inversely with load; this preventsexcessive power demands with heavy loads and provides desirable highspeeds at light loads.

The circuits employed almost universally for control of DC. crane motorscomprises a series connection for hoisting with various resistors inseries that may be incrementally removed to increase the speed ofhoisting. The series connection will not work for lowering as anoverhauling load would cause the motor to run away. Therefore, byconnecting the armature and field in parallel, with resistance in eachcircuit, characteristics approaching a shunt motor are obtained. With alight load the motor drives the hook down taking a relatively heavycurrent from the line. When the load is sufficient to overcome thefriction of the drive, it begins to overhaul the motor, which then actsas a generator and retards the load by the associated motor effectagainst the direction of rotation. The speed of lowering may then bechanged by varying the resistance in either the series field or thearmature circuit to vary this retarding motor effect. While there aremany different controls provided by different manufacturers, all operateon the same general principles, i.e., varying series resistance on thehoist cycle to change speed and varying resistance in the field orarmature circuits for speed control on the lowering cycle.

It is to be understood that an overhauling load is one which will causethe armature speed, when the motor is operating in the loweringdirection, to increase to the point where the generated counterelectromotive force exceeds the line voltage and the motor operates as agenerator.

For a detailed circuit operation of a dynamic lowering control,reference is made to Chapter 13 of Control of Electric Motors by P. B.Harwood, John Wiley & Son, Inc., New York. This description applies to aCutler- Hammer controller of the same type described hereinbelow forillustrative purposes with the apparatus of this invention.

Most crane hoist equipment contains many standard safety features suchas the series magnetic brake which allows the cable drum or armature toturn only when there is power available to operate the motor and releasethe brake shoe. Also the off position on most controllers automaticallyshort circuits the field and armature to give dynamic braking to controlthe load partially in the event that the magnetic brake should fail.Limit switches to avoid over-hoisting are also well known and operate onobvious principles. Overload relays are also commonly used to open themotor circuit in the event of unusually high currents due to heavyloads. Most equip ment utilizing dynamic lowering also has means forlimiting the amount of resistance which can be inserted in the fieldcircuit when an overhauling load is being lowered. This limits minimumfield strength, and thus limits the maximum lowering speed.

When the crane is lowering with an overhauling load, the motor effectdue to the generator action is the only retarding effect on load speed.If an open should occur in the shunt armature circuit, no current canflow, therefore, the braking or retarding force is lost and the loadrapidly runs away. In the majority of cases, the operator does not havetime to move the controller to the off position before the load gainssuch momentum that the magnetic brake is unable to stop it.

In the past, complicated systems were sometimes used comprising extratrolley rails, brake shoes, commutators, etc. However, these safetydevices were often the cause themselves of equipment failure andshutdown. Due to the failure of such attempts, this form of safetyprotection is not available on most standard controllers. However,experience has taught that in corrosive atmospheres as, for example,metallurgical plants, such failures do occur and can be disastrous toboth equipment and personnel in the area.

It is, accordingly, an object of the present invention to provide aprotective device for guarding against discontinuities in the shuntarmature circuit of direct current crane hoist motors which is simple,rugged and dependa e.

It is a further object of the present invention to provide a safetydevice for use with direct current crane hoist motors utilizing dynamiclowering whereby power is removed from the motor whenever an opencircuit condition occurs in the shunt armature circuit during saiddynamic lowering.

It is a still further object of the present invention to provide such asafety device for a crane hoist motor operating from a two-wire directcurrent source.

Other objects and advantages will be apparent from the followingdescription and drawings in which:

FIG. 1 is a schematic showing the protective device of the presentinvention used with a two-wire, direct current, hoist control system;and

FIG. 2 is a simplified schematic of the actual electrical circuitsactuated in the various positions of the controller.

According to the teachings of this invention, a protective device isprovided for a direct current hoist motor and controller thereforutilizing dynamic lowering, which interrupts the motor power supply inthe event of any discontinuity in that portion of the shunt armaturecircuit which is in circuit with the field circuit during lowering.

It is to be understood that the subject matter of this invention isintended for use Wllth direct current hoist motors utilizing dynamiclowering. Alternating current motors for this application are either ofthe simple squirrel-cage type or slip ring induction type and do notdevelop voltages or polarities suitable to operate such a protectivedevice as disclosed.

The term shunt armature circui as used in the specification and claimsrefers to the circuit including the p 3 motor armature winding whichshunts the series field, the series brake and the associated speedcontrol resistors which are employed when the motor is operated in thelowering direction.

Referring more particularly to FIGURE 1, the protective device of thepresent invention comprises a 250 volt direct current relay 10 havingnormally closed contacts, one to 2000 ohm, 200 watt variable resistor46,

one 216 to 240 mid. capacitor 44, and a normally closed contact 58a.Contactor 53a is operated by coil 58 in the controller, whichdisconnects the protective device from the circuit during hoistingoperation.

In the invention, the protective device is connected,

during lowering, directly in parallel with that portion of the shuntarmature circuit to be protected. This portion is shown in the drawingas being between the points 24 and 30 and includes the motor armaturewinding, the series field, the series brake and associated resistors.The resistor 46 is adjusted to the maximum value whereby the relay coilwould be actuated by any discontinuity in the shunt armature circuitbetween points 24 and 30.

Upon the occurrence of a discontinuity in the shunt arrnature circuit,exclusive of the motor armature winding the voltage across the relaycoil 10 will increase and thereby cause relay coil 10 to be activated.The activa' tion of relay coil 16 operates oontactor 10a in the holdcircuit of the controller. The hold circuit comprises relay coil 35 andits associated contact-s one of which, 35a, deenergizes relay coils 28and 48 whose contacts, 28a and 48a, respectively remove power from themotor, thus other than those embodied by the While this invention hasbeen described with respect to the particular controller as used byCutler-Hammer, Inc, as described in the previously-mentionedpublication, it is to be understood that it would operate equally wellwith any direct currentcrane hoist motor utilizing dynarnic lowering.

While the invention has been described in a detailed manner with respectto certain embodiments as shown by the drawings, it is to be understoodthat modifications may be made in the control circuit and that nolimitations scope of the appended claims are intended.

What is claimed is:

In combination with a direct current hoist motor and controller thereforsupplied by a two-wire line, said controller being adapted to provideseries operation for hoisting and shunt operation for dynamic loweringwhereby in shunt operation the motor field winding is paralleled by ashunt circuit which includes the motor. armature winding, a magneticbrake and electrical resistors; a protective device operable in theevent of a discontinuity in the shunt circuit external to the motorarmature winding, said device comprising relay means connected acrosssaid shunt circuit, said relay means having associated con tactor meansarranged to remove power from the entire motor when the relay isactuated.

References Cited by the Examiner UNITED STATES PATENTS 1,713,202 5/29Warner 31713 2,421,080 5 47 Newman 318-247 2,721,300 10/55 Myles 317-13OTHER REFERENCES James H. D. and Markle, L. E., Controllers for ElectricMotors, Second Edition, pages 29-31, McGraw-Hill, New York, 1952.

JOHN F. COUCH, Primary Examiner.

MILTON O. HIRSHFIELD, Examiner.

